The present invention relates generally to operations performed in conjunction with a subterranean well and, in an embodiment described herein, more particularly provides a method of gravel packing a wellbore.
It is sometimes the case that gravel packs have voids, rather than being completely packed with gravel, in an annulus between a well screen assembly and a wellbore. Voids in a gravel pack are very undesirable, since formation fines can travel through the voids to the well screens, thereby defeating the purpose for performing the gravel pack operation.
Typically, voids are caused when there is a decrease in flow velocity while a slurry is being pumped into the annulus. The velocity decrease permits some of the gravel to fall out of the slurry flow and accumulate in the annulus. This accumulated gravel may bridge off and prevent further gravel transfer through the annulus.
The problem is exacerbated by the fact that it is standard practice to gravel pack an entire interval at one time. That is, a gravel slurry is flowed into the annulus between the wellbore and a long gravel packing assembly including multiple well screens. The assembly is many times hundreds of feet long.
It will be readily appreciated that this slurry flow through such a long annulus provides ample opportunity for flow velocity fluctuations, including velocity decreases due to, for example, fluid loss into the formation, fluid flow into the many well screens, etc. The problem is further exacerbated where the wellbore is substantially deviated or horizontal. It is quite common to use very long screen assemblies in horizontal wells.
Thus, it may be seen from the foregoing that it would be advantageous to provide a method of gravel packing a wellbore which solves the problem of voids forming in a gravel pack.
In carrying out the principles of the present invention, in accordance with an embodiment thereof, a method of gravel packing is provided which is a significant advance over prior methods. The method enables a continuous zone to be gravel packed in successive individual sections, thereby eliminating the problems associated with attempting to flow gravel into the entire zone.
In a described embodiment, multiple well screens are positioned in a wellbore. A continuous portion of the wellbore is isolated using, for example, one or more packers, with the well screens being disposed in the isolated portion. The isolated wellbore portion is then progressively gravel packed in successive individual predetermined sections of the isolated wellbore portion.
In one aspect of the method, the method includes the step of opening successive ones of the well screens for fluid flow through the filtering material of the respective well screens. The liquid portion of a slurry is flowed only through the filtering material of well screens which have been opened to such flow. The well screens are opened successively, so the slurry flows toward the well screens in succession, rather than to all of the well screens at once.
In another aspect of the invention, the method includes the step of alternating the well screens with valves in the isolated wellbore portion. Successive ones of the valves are opened, thereby progressively depositing gravel from a tubular string, through the opened valves, and into corresponding predetermined sections of the wellbore. By opening the valves in succession, the gravel enters the wellbore sections progressively.
In yet another aspect of the invention, the method includes the step of opening corresponding successive valves and well screens, thereby successively gravel packing preselected sections of the wellbore portion. The opening of the valves and opening of the well screens are coordinated, so that gravel enters a wellbore section through a valve corresponding to a well screen which has also been opened to fluid flow therethrough. This coordination of both slurry delivery and fluid return enables the wellbore sections to be successively gravel packed.
In still another aspect of the invention, the method includes the step of using a selective slurry diversion device to accomplish the coordination of slurry delivery and fluid return. In one embodiment, the slurry diversion device is activated in response to predetermined pressure levels in the slurry delivery flow passage, to selectively divert the gravel slurry into successive predetermined sections of the wellbore portion. The slurry diversion device may include multiple valves, may include one or more hydraulic metering devices for operating the valves, may include individual valve actuators, may include a plug which displaces through the slurry delivery passage, or any other means of diverting slurry flow.
These and other features, advantages, benefits and objects of the present invention will become apparent to one of ordinary skill in the art upon careful consideration of the detailed description of representative embodiments of the invention hereinbelow and the accompanying drawings.